. the clash was loud. >> go, scott brown. >> reporter: and sometimes angry outside. >> you're delusional! >> reporter: inside the arena a tense duel between republican senator scott brown and harvard professor democrat elizabeth warren. >> excuse me, i'm not a student in your classroom, please let me respond, okay? thank you. >> reporter: led by moderator of "meet the press" david gregory who took on the candidates' nasty running battle and campaign ad war. >> professor warren got caught in a lie. >> reporter: whether warren used her native american heritage to gain any employment advantage with law school. >> do you consider yourself a minority? >> i listed myself as native american. i was listed there. it's part of who i am. >> reporter: brown argues that warren has not told voters why she switched between calling herself native american on applications. >> she changed her nationality to native american. >> reporter: and later referred to herself as white. >> at the pinnacle of her success when she became tenured at harvard she changed back to being white. >> are you hiding something?